The present invention is directed to several washer configurations useful in clamping plastic members to a metal substrate.
In recent years, technology has developed plastics with vastly improved strength characteristics. Accordingly, plastics have found an ever increasing number of industrial uses. The applicance and automotive industries, for example, are increasing their use of plastics in an effort to reduce the overall product weight.
One perplexing problem facing plastics users is how to fasten it. When subjected to normal clamp loading particularly where the joint may be subject to heat caused by friction or the like, most plastics will "cold flow" or "creep", that is, the plastic will move laterally under load to avoid the compression, thereby loosening the joint. Such fastening problems have prevented, until now, plastics from being utilized in applications where the plastic needs firm clamping for lateral stability such as plastic wheels, for example.
One solution to the plastic clamping problem is described in co-owned U.S. Pat. No. 4,193,434. The fastener-washer assembly disclosed there has proven highly successful in solving many plastic clamping problems in a wide variety of applications. However, in instances where it is necessary to subject the plastic member to greater clamp loading or where special constraints will not permit a washer of that type to be used, alternate devices are needed.
The present invention provides devices to meet those needs. In each embodiment, a polygonal washer forms a large surface area over which to distribute the clamp load. A projecting member has sufficient length to extend through the thickness of the plastic to engage a metallic substrate therebeneath. Therefore, a portion of the clamp load is absorbed in a metal-to-metal connection. Further, various spring characteristics are built into the washer which require additional force to overcome. Lastly, this metal-substrate-engaging member is non-centrally or asymmetrically positioned so that the washer will pivot thereabout distributing the remainder of the clamp load over a broad surface area which is positioned well away from the bolt-receiving hole in the plastic.
Other characteristics, features and advantages of the present invention will become apparent by reading the following specification in conjunction with the accompanying drawings.